001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.pool2;
018
019/**
020 * A simple base implementation of {@link ObjectPool}.
021 * Optional operations are implemented to either do nothing, return a value
022 * indicating it is unsupported or throw {@link UnsupportedOperationException}.
023 * <p>
024 * This class is intended to be thread-safe.
025 * </p>
026 *
027 * @param <T> Type of element pooled in this pool.
028 *
029 * @since 2.0
030 */
031public abstract class BaseObjectPool<T> extends BaseObject implements ObjectPool<T> {
032
033    private volatile boolean closed;
034
035    /**
036     * Not supported in this base implementation. Subclasses should override
037     * this behavior.
038     *
039     * @throws UnsupportedOperationException if the pool does not implement this
040     *          method
041     */
042    @Override
043    public void addObject() throws Exception, UnsupportedOperationException {
044        throw new UnsupportedOperationException();
045    }
046
047    /**
048     * Throws an {@code IllegalStateException} when this pool has been
049     * closed.
050     *
051     * @throws IllegalStateException when this pool has been closed.
052     *
053     * @see #isClosed()
054     */
055    protected final void assertOpen() throws IllegalStateException {
056        if (isClosed()) {
057            throw new IllegalStateException("Pool not open");
058        }
059    }
060
061    @Override
062    public abstract T borrowObject() throws Exception;
063
064    /**
065     * Not supported in this base implementation.
066     *
067     * @throws UnsupportedOperationException if the pool does not implement this
068     *          method
069     */
070    @Override
071    public void clear() throws Exception, UnsupportedOperationException {
072        throw new UnsupportedOperationException();
073    }
074
075    /**
076     * {@inheritDoc}
077     * <p>
078     * This affects the behavior of {@code isClosed} and
079     * {@code assertOpen}.
080     * </p>
081     */
082    @Override
083    public void close() {
084        closed = true;
085    }
086
087    /**
088     * Not supported in this base implementation.
089     *
090     * @return a negative value.
091     */
092    @Override
093    public int getNumActive() {
094        return -1;
095    }
096
097    /**
098     * Not supported in this base implementation.
099     *
100     * @return a negative value.
101     */
102    @Override
103    public int getNumIdle() {
104        return -1;
105    }
106
107    @Override
108    public abstract void invalidateObject(T obj) throws Exception;
109
110    /**
111     * Has this pool instance been closed.
112     *
113     * @return {@code true} when this pool has been closed.
114     */
115    public final boolean isClosed() {
116        return closed;
117    }
118
119    @Override
120    public abstract void returnObject(T obj) throws Exception;
121
122    @Override
123    protected void toStringAppendFields(final StringBuilder builder) {
124        builder.append("closed=");
125        builder.append(closed);
126    }
127}